Skip to main content

Full text of "Handbook Of Chemical Engineering - I"

See other formats


POWER GENERATION AND TRANSMISSION
39
delivery to burners. Assuming a minimum tank temperature of 30, with exhaust steam as the heating agent, the transmitting surface necessary (which may be wrought iron pipe) is about 1 sq. in. per pound of oil per hour if the oil velocity in the tube is to be kept down to the point where the pumping head is reasonable. The weight of steam will be about one twentieth the weight of oil.
Burners are usually operated by steam or compressed air, the former involving simpler and cheaper equipment but possibly a somewhat greater operating cost, since up to 4 per cent of all the steam generated will be expended in atomizing the oil. This is high-pressure steam, and the necessary make-up feed water must be supplied, A common pressure for oil fed to steam-operated burners is 30 Ib. gage, maintained bj a pressure regulator on the pump. Ample straining should be provided with provision for cleaning strainers without interrupting operation. Burners should be made so as to be readily cleaned, with provision for easy renewal of tips. A single burner will discharge enough oil for a 400-hp. boiler. Automatic regulation of steam pressure and oil delivery in proportion to the load is desirable.
Oil permits of a closely regulated air supply and high furnace temperature. The requirements for good combustion are similar to those for highly volatile soft coals (p. 35). It is important that the intense heat be well distributed and to avoid the blowpipe effect due to impingement from the burner on metal or brickwork. This often leads to the use of two burners, where one would have sufficient capacity. It also explains the furnace design illustrated. This has the "back shoot" burner, the air being admitted through checkerwork. Peepholes through the furnace walls are desirable.
The fire risk is minimized by isolating the main storage tanks, providing a smothering steam supply to the inside of all tanks, and avoiding overheating of the fuel. Gas tar is burned like oil. It is particularly heavy and has a low flash-point, so that the temperature must be carefully adjusted. Its heat value is around 14,000 B.t.u. per pound.
MISCELLANEOUS SOLID FUELS
		Composition,	per cent	
	Carbon	Ash	Moisture	B.t.u. per pound
Peat	35, drv	3 to 36	6 to 20, air-dried	6 000 to 10 000 dry
Wood           .......	50, dry	Usually<l	18 to 60	8 000 to   9,000, dry
Straw           .......	36, dry	5	16	5 , 000 to   6 , 500, wet
Shelled corn .......				7 , 800 to   8 , 500, dry
Charcoal	84	3	12	12 850
Bagasse ...........	43 to 47	11A to 3	40 to 54	8,000, dry
Tan bark ..........	52, dry	1.4, dry	66	9,500, dry
Wood comes next to cellulose in the progressive series from that compound to anthracite. It is available as cord wood, slabs, edgings and refuse, the last being often "hogged " to shreds. A cord of hemlock weighs 1,200 Ib.; of hickory, 4,500 Ib. The soft woods are the higher in heat value. Woods contain about 6 per cent of hydrogen and under 1 per cent of nitrogen. Rates of combustion for refuse should be high (150 Ib.) and a strong natural draft used. Extension furnaces are essential for driving off moisture. Large furnace space, a thick fuel bed and an undisturbed fire are recommended. Refuse should be chuted to